Geldanamycin is a macrocyclic lactam that is a member of the benzoquinone-containing ansamycins family of natural products. The isolation, preparation and various uses of geldanamycin are described in U.S. Pat. No. 3,595,955. Like most naturally-occurring members of this class of molecules, geldanamycin is typically produced as a fermentation product of Streptomyces hygroscopicus var. geldanus var. nova strain (Journal of Antibiotics Vol. 23, Page 442 (1970)). Other analogs and derivatives of geldanamycin have been identified or synthesized, and their use as antitumor agents is described in U.S. Pat. Nos. 4,261,989 and 5,387,584, and published PCT applications WO 00/03737 and WO 03/072794. One member of this family that has been examined in some detail is 17-allylamino-17-demethoxygeldanamycin (“17-AAG”). Geldanamycin and its derivative have been shown to bind to HSP90 and antagonize the protein's activity.
HSP90 is a highly abundant protein which is essential for cell viability and it exhibits dual chaperone functions (J. Cell Biol. (2001) 154:267-273, Trends Biochem. Sci. (1999) 24:136-141). It plays a key role in the cellular stress response by interacting with many proteins after their native conformation has been altered by various environmental stresses, such as heat shock, ensuring adequate protein folding and preventing non-specific aggregation (Pharmacological Rev. (1998) 50:493-513). In addition, recent results suggest that HSP90 may also play a role in buffering against the effects of mutation, presumably by correcting the inappropriate folding of mutant proteins (Nature (1998) 396:336-342). However, HSP90 also has an important regulatory role under normal physiological conditions and is responsible for the conformational stability and maturation of a number of specific client proteins, of which about 40 are known (see. Expert. Opin. Biol Ther. (2002) 2(1): 3-24). These can be subdivided into three groups: steroid hormone receptors, serine/threonine or tyrosine kinases and a collection of apparently unrelated proteins, including mutant p53 and the catalytic subunit of telomerase hTERT. All of these proteins play regulatory roles in physiological and biochemical processes in the cell.
HSP90 antagonists are currently being explored in a large number of biological contexts where a therapeutic effect can be obtained for a condition or disorder by inhibiting one or more aspects of HSP90 activity. Although the primary focus has been on proliferative disorders, such as cancers, other conditions are showing levels of treatment using HSP90 antagonist. For example, U.S. Published Patent Application 2003/0216369, discloses the use of HSP90 inhibitors for treatment of viral disorders. HSP90 inhibitors have also been implicated in a wide variety of other utilities, including use as anti-inflammation agents, agents for treating autoimmunity, agents for treating stroke, ischemia, cardiac disorders and agents useful in promoting nerve regeneration (See, e.g., WO 02/09696 (PCT/US01/23640); WO 99/51223 (PCT/US99/07242);U.S. Pat. Nos. 6,210,974 B1; and 6,174,875). There are reports in the literature that fibrogenetic disorders including but not limited to scleroderma, polymyositis, systemic lupus, rheumatoid arthritis, liver cirrhosis, keloid formation, interstitial nephritis, and pulmonary fibrosis may be treatable using HSP90 inhibitors. (Strehlow, WO 02/02123; PCT/US01/20578).
Geldanamycin's nanomolar potency and apparent selectivity for killing tumor cells, as well as the discovery that its primary target in mammalian cells is HSP90, has stimulated interest in its development as an anti-cancer drug. However, the extremely low solubility of these molecules and the association of hepatotoxicity with the administration of geldanamycin has led to difficulties in developing an approvable agent for therapeutic applications. In particular, geldanamycin has poor water solubility, making it difficult to deliver in therapeutically effective doses.
More recently, attention has focused on 17-amino derivatives of geldanamycin, in particular 17-AAG, that show reduced hepatotoxicity while maintaining HSP90 binding. See U.S. Pat. Nos. 4,261,989; 5,387,584; and 5,932,566. Like geldanamycin, 17-AAG has very limited aqueous solubility. This property requires the use of a solubilizing carrier, e.g., egg phospholipid with DMSO, or Cremophore® (BASF Aktiengesellschaft), a polyethoxylated castor oil; the presence of either of these carriers results in serious side reactions in some patients.
Consequently, there remains a need to discover more soluble analogs of benzoquinone-containing ansamycins and specific and general methods for creating them, particularly geldanamycin and its analogs, such as 17-AAG.